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Antonio Salgado Carmen Varela Ana María García Collazo Paolo Pevarello 《Magnetic resonance in chemistry : MRC》2010,48(8):614-622
The condensation of malonoaldehyde derivatives with either a 3‐amino‐[1,2,4]‐triazole or a 3,5‐diamino‐[1,2,4]‐triazole precursor was studied. In agreement with previous reports, two different bicycles, namely, bearing the regioisomeric [1,2,4]triazolo[1,5‐a]pyrimidine ( 1 ) or[1,2,4] triazolo [4,3‐a]pyrimidine ( 2 ) structural surrogates, could be obtained. We found that, depending on the triazole precursor, only one regioisomer resulted, either of the 1 or 2 series. We also observed that these two structural surrogates could be unambiguously differentiated by indirectly measuring their 15N chemical shifts by 1H? 15N HMBC experiments. The occasional conversion of [1,2,4]triazolo[4,3‐a]pyrimidines to the [1,2,4]triazolo[1,5‐a]pyrimidine counterparts could be unequivocally determined by 15N NMR data. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Five synthetic oxyhydroxides of iron with different contents of Al and an approximately fixed content of Ni have been studied using57Fe Mössbauer spectroscopy in conjunction with X-ray diffraction, infrared spectroscopy, transmission electron microscopy and chemical analysis. It has been shown that, besides alumogoethite, some amorphous Al-bearing phase of iron exists, Ni being preferentially associated with this phase. Not only the effective magnetic field, but also the line width of the Mössbauer spectra at 77 K may be a measure of Al content in both phases. Doublet to sextet area ratio provides a measure of the relative concentration of the amorphous and crystalline phases. 相似文献
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Arnaldo Alzrreca Mayra Avils Luis Collazo Antonio Prieto 《Journal of heterocyclic chemistry》1990,27(6):1729-1731
The thermal cyclization of a dihydroxyketone equivalent 4b leads to the predominant formation of crystalline 4-(benzenesulfonyl)-1,6-dioxaspiro[4.5]decane ( 8 ). Under similar reaction conditions the tetrahydrofuranylidene derivative 6 is obtained from ketone 4c . It does appear that the phenylsulfonyl group is a factor which influences the course of the reaction leading to the preferential formation of one of the possible stereoisomers. 相似文献
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N. Govindaraju A. Aleksov X. Li F. Okuzumi S.D. Wolter R. Collazo J.T. Prater Z. Sitar 《Applied Physics A: Materials Science & Processing》2006,85(3):331-335
Superior thermal conductivity, high resistance, high breakdown voltage and wide band gap make diamond an attractive material for a variety of applications in electronics. One of its most appealing applications is as a buried dielectric in silicon-on-diamond (SOD) technology. This paper presents thermal conductivity measurements conducted on a series of diamond films (grown by the microwave plasma chemical vapor deposition technique) as a function of the sample morphology and thickness, for eventual incorporation in the SOD structures. Results show that there is a significant difference in the measured thermal conductivity between samples with fiber texture and samples with sheet texture. Also, measurements performed on a 160-μm-thick diamond sample before and after reactive ion etching of approximately 10 μm of the nucleation layer show no significant change in the measured value of the thermal conductivity. PACS 81.05.Uw; 65.40.-b; 61.72.-y 相似文献
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García-Castro D. Ajoor M. Alvarez-Pol H. Blanco A. Cabanelas P. Callón-Rivas J. Collazo J. Clemencio F. Cuenca-García J. J. Cruces M. Fonte P. Fontenla Y. Flores J. Garzón J. A. Gomis-Moreno A. Iglesias A. Kornakov G. Kurtukian-Nieto T. Lopes L. Loureiro C. Pazos A. Rodríguez C. Saraiva J. P. Seco M. Valladares M. Villasante-Marcos V. Xuna J. 《Physics of Atomic Nuclei》2021,84(6):1070-1079
Physics of Atomic Nuclei - The TRASGO project develops high resolution tracking detectors, sensitive to single electrons and muons as well as to bundles of both kinds of particles. Two detectors... 相似文献
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Mark D. Losego Seiji Mita Ramon Collazo Zlatko Sitar Jon-Paul Maria 《Journal of Crystal Growth》2008,310(1):51-56
Molecular beam deposition systems allow for unparalleled control of film composition and structure. This article addresses the capacity for controlling metal and oxidant fluxes in the Yb/O2 system to access the metastable phase ytterbium monoxide (YbO). Experiments exploring the growth of polycrystalline YbOx films by molecular beam deposition demonstrate that a 2:1 molar ratio of Yb:O2 fluxes is necessary to achieve preferential growth of the divalent oxide. Applying similar deposition conditions to a (0 0 1) GaN surface leads to the growth of epitaxial (1 1 1) YbO films. Similar to other rocksalt oxides grown on GaN surfaces, YbO films display a 3D growth mechanism that leads to a grainy morphology with crystallites of 50 nm lateral dimensions. Rocking curves in ω and φ have full-width half-maximum values of 1.77° and 4.1°, respectively; further improvements in crystal quality appear to be limited by the thermal stability of the YbO phase. 相似文献
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This paper studies unsteady laminar flow of dusty conducting fluid between parallel porous plates with temperature dependent
viscosity and the Network Simulation Method (NSM) is used to solve the governing nonlinear partial differential equations.
The fluid is acted upon by a constant pressure gradient and an external uniform magnetic field is applied perpendicular to
the plates that are assumed to be porous. The NSM is applied to solve the steady-state and transient problems of flow and
heat transfer for both the fluid and dust particles. With this method, only discretization of the spatial co-ordinates is
necessary, while time remains as a real continuous variable. The velocity and temperature are studied for different values
of the viscosity and magnetic field parameters. 相似文献
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